Devices such as laser diode drivers, thermoelectric cooler (TEC) controllers and the like, need a source of AC or DC current with an acceptable level of stability and noise. Low noise current sources generally need to deliver AC or DC current, based on an input signal, with an acceptable level of stability and noise. Such current sources typically require the use of a current regulator, which may be a transistor. Depending on the output current and voltage drop across the current regulator, there may be significant heat generated by the current regulator which must then be dissipated by a heat sink or other suitable device. In addition, for applications where the output current must have low noise, a voltage regulator may be required in the current source to reject or otherwise suppress the power supply ripple. The voltage regulator may also have a heat sink to dissipate heat generated by a voltage drop across the voltage regulator.
One conventional way to design a current source uses an unregulated power supply connected to a voltage regulator which is in turn coupled to a current regulator. Both the voltage regulator and the current regulator may be transistors. In such a system, power dissipates independently, and typically, unevenly on the heat sinks of the voltage regulator and current regulator, making the power dissipation inefficient. Another conventional design for a current source uses an unregulated power supply to provide power to a transistor that is used for a current regulator without the use of a voltage regulator. However, this system has only one heat sink for heat dissipation which is coupled to the current regulator. In addition, the voltage drop on the current regulator must be high enough to reduce the ripple noise of the input power, and this leads to more power dissipation in the single heat sink. These factors may also result in an inefficient dissipation of excess power in the current source.
Some other methods use a switching power supply to power the current regulator. Sometimes the switching power supply is adjusted by software or calibration to maintain the minimum voltage drop on the current regulator and minimize dissipation. The heat is then at least partially dissipated in the switching power supply. The disadvantage of using a switching power supply that supplies power directly to the current regulator is the noise that is produced in the output current. The prior art systems and methods either produce uneven power dissipation between the various components, or produce noise in the regulated current. What has been needed is a low noise current supply with efficient heat dissipation.